The major objective is to specify the quantitative and qualitative relations between physical characteristics of noise and the temporary hearing losses produced by the noise. Knowledge of these relations for human observers will permit the specification of levels of noise that will not injure the inner ear, will help produce a temporary hearing loss, and will not delay the decay of an existing hearing loss. In addition, these relations will provide scientific bases for the development of noise standards and criteria. Human observers will be exposed to low levels of continuous and intermittent noises for a period of up to 48 to 1 hrs. Auditory sensitivity for pure tones as well as other tests of auditory function will be measured before an exposure, during quiet periods interspersed within an exposure, and after an exposure. Results will be evaluated with respect to previous human and sub-human data, a predictive model (the Equivalent Power Model), and current noise standars and criteria. Collectively, the proposed experiments will provide a parallel to earlier and current animal experiments and aid in elucidating the mechanisms of hearing and loss.